1. Field of the Invention
The present invention relates generally to fluid nozzles for use on a drill bit. More specifically, the present invention relates to an improved nozzle and method of using compression torque forces to engage and disengage the nozzle and bit.
2. Description of the Prior Art
Wells used to extract hydrocarbons from the earth are formed using drill bits that are rotated by a length of drill pipe from a drilling rig located at the well surface. Drilling fluid is pumped through the drill string to the bit, where it exits the bit into the wellbore. The fluid serves to cool and lubricate the bit and to return the formation bit cuttings back to the well surface.
The drill bit is equipped with nozzles that control the exiting fluid velocity, direction, and pattern of flow. The nozzle is typically threadedly engaged within a receptacle in the bit body and has a central flow passage that communicates with the drilling fluid supplied through the drill string. The nozzle is fabricated of a material, such as tungsten carbide, that can withstand the erosive forces resulting from the flow of the high pressure, abrasive drilling fluids. The nozzles are removable to permit replacement, as well as to allow a variety of different nozzles having different flow characteristics to be employed with a particular bit.
Material such as tungsten carbide, while well suited for withstanding the effects of erosion, is extremely brittle and subject to breakage. Torque forces applied to the nozzle while seating or withdrawing the nozzle from a bit must be controlled to prevent nozzle breakage. The brittleness of the material also makes the nozzle subject to breakage as a result of fractures that originate at stress concentration points, such as occur at the intersection of planar surfaces in the nozzle drive area. Prior art nozzle designs have addressed the problems of breakage by employing relatively large amounts of tungsten carbide material in the nozzle drive area.
Damage to the drive area of the nozzle is to be avoided because of the danger of creating stress concentration points that reduce the drive area strength. Such damage can occur, for example, during application of the nozzle to the bit, or from fluid erosion of the surfaces of the drive area, or from die adhesions occurring during the fabrication of the nozzle. In fabricating the nozzle, a powder material that includes tungsten carbide is typically compacted into a die having the desired nozzle shape and then heated to a temperature that converts the powdered material into a hard, solid body. During this heating process, the compacted material shrinks in volume and draws away from the surrounding die. Many conventional nozzle drive area surfaces are essentially parallel to the axis of the nozzle and tend to adhere to the die surface as the nozzle form moves axially during the shrinking process. These adhesions cause material to break away from the drive area of the nozzle, resulting in a defective drive area. It is desirable in the design of such bodies to minimize the number of such parallel surfaces to reduce the frequency of defective nozzle formations.
Conventional nozzles are rotated into the threaded bit receptacle with the aid of a drive tool that engages a drive area structure formed on the fluid exit end of the nozzle. This drive area structure typically may take the form of a slot designed to be engaged by a blade-type tool or a multisided opening designed to be engaged by an allen wrench-type tool. Other tool-engaging drive area designs are also used, each generally requiring that a tool be engaged with a drive surface that prevents relative rotation between the tool and the nozzle so that torque is imparted to the nozzle as the tool is rotated.
The drive area structures in such prior art nozzles are subjected to tensile stresses as the tool is rotated by the drive tool. Forces that exceed the tensile limits of the drive area structure can cause the nozzle to break. If the amount of material employed in the drive area of the nozzle is increased to accommodate greater torque forces, the flow passage dimensions extending through the drive area must be decreased. It is desirable to employ as little material as possible in a nozzle to keep material costs as low as possible and to keep the nozzle size as small as possible.